This city I've been constructing is situated for the larger percentage underground with some smaller structures and other features laying above on ground level. Seeing as the majority is submerged it is fairly dark and gloomy, however there are various different light sources situated around the main objects. As you descend down the spiral staircase you enter a huge underground cavern which branches off into currently 3 different areas/caverns each with unique features. There is a lot of detail in what is currently completed. There are lots of passageways, fully decorated buildings, externally and internally and a few complex mineshafts with connecting railways which are fully ride able. (One of them allows you to travel from the depths all the way to the surface and through a huge mountainous system on ground.) There are hundreds of features in this build and many more to come.
Oh yeah, and not forgetting the huge fortress situated in a cavern even larger than the central area. :)